The present disclosure generally relates to ceramic catalysts and in particular, to high surface area ceramic catalysts.
With the decline of gaseous chlorine as a microbiocide, various alternatives have been explored, including bleach, bleach with bromide, bromochlorodimethyl hydantoin, ozone, and chlorine dioxide (ClO2). Of these, chlorine dioxide has generated a great deal of interest for control of microbiological growth in a number of different industries, including the dairy industry, the beverage industry, the pulp and paper industries, the fruit and vegetable processing industries, various canning plants, the poultry industry, the beef processing industry, and miscellaneous other food processing applications. Chlorine dioxide is also seeing increased use in municipal potable water treatment facilities and in industrial waste treatment facilities, because of its selectivity towards specific environmentally-objectionable waste materials, including phenols, sulfides, cyanides, thiosulfates, and mercaptans. In addition, chlorine dioxide is being used in the oil and gas industry for downhole applications as a well stimulation enhancement additive.
Unlike chlorine, chlorine dioxide remains a gas when dissolved in aqueous solutions and does not ionize to form weak acids. This property is at least partly responsible for the biocidal effectiveness of chlorine dioxide over a wide pH range, and makes it a logical choice for systems that operate at alkaline pH or that have poor pH control. Moreover, chlorine dioxide is a highly effective microbiocide at concentrations as low as 0.1 parts per million (ppm) over a wide pH range.
The biocidal activity of chlorine dioxide is believed to be due to its ability to penetrate bacterial cell walls and react with essential amino acids within the cell cytoplasm to disrupt cell metabolism. This mechanism is more efficient than other oxidizers that “burn” on contact and is highly effective against legionella pneumophilia, algae and amoebal cysts, giardia cysts, coliforms, salmonella, shigella, various viruses, and cryptosporidium.
Unfortunately, chlorine dioxide in solution is unstable with an extremely short shelf life and thus, is not commercially available. Chlorine dioxide must typically be generated at its point of use such as, for example, by a reaction between an aqueous solution of a metal chlorate salt or metal chlorite salt and a strong acid. To increase the yield, it oftentimes is desirable to employ a catalyst.
Catalysts, which may generally take the form of heterogeneous, homogeneous, or biological catalysts are of significant importance to the chemical industry as evidenced by the fact that the great majority of all chemicals produced have been in contact with a catalyst at some point during their production. Despite the many advances in the areas of homogeneous and biological catalysis, heterogeneous catalysts remain the predominant form used by industry. Heterogeneous catalysts are favored in part because they tolerate a much wider range of reaction temperatures and pressures, they can be more easily and inexpensively separated from a reaction mixture by filtration or centrifugation, they can be regenerated, and they are less toxic than their homogeneous or biological counterparts.
Heterogeneous catalysts utilized in chlorine dioxide generation processes are generally a granular solid material that operates on reactions taking place in the gaseous or liquid state, and generally includes a reactive species and a support for the reactive species. Deposition of the reactive species (i.e., the catalyst) onto the support generally includes numerous processing steps. Typically, the support is obtained separately upon which the catalyst is deposited and activated. For example, commercially available ceramic particles are first obtained and backwashed with water to remove fines. The backwashed ceramic particles are then baked at an elevated temperature (e.g., 50°) to remove residual water. Preparation of the catalyst material then includes contacting the support with a catalyst precursor to form active metal catalyst sites, for example, a catalyst precursor salt. For example, a metal oxide precursor salt is dissolved in an aqueous solution including an alcohol, and the solution is then coated onto the support. Depending on the desired properties, a solution of the metal oxide precursor salt may contain further additives, for example, ions that increase the solubility of the metal oxide precursor. Alternatively, the metal catalyst may be deposited onto the support material using other techniques such as impregnation, coprecipitation, ion exchange, dipping, spray coating, vacuum deposition, sputtering or the like. In addition, it is generally known that the catalyst activity of the catalyst material is improved with multiple depositions (i.e., the metal oxide precursor solution is applied by several individual depositions).
The metal deposited onto the support by the precursor solution is then thermally or chemically oxidized to the oxide form. For example, the catalyst material can be calcined in excess of 500° C. in an oven, which allows the precious metal salt to convert to its active oxide form. The catalyst material is then cooled and in order to increase the number of active site, some of the above noted steps may be repeated. In summary, the prior art processes for preparing catalyst material suitable for use in chlorine dioxide processing involved numerous steps, requiring a significant amount of time.
Accordingly, there remains a need for improved methods of making the catalyst material.